Efficiency of shape memory alloy seismic restrainers for several conditions of bridge joints

Movement joints are needed in bridges to accommodate longitudinal expansion and contraction. Enough joint width needs to be available to accommodate not only longitudinal expansion but also expected movements of joints during earthquakes. This may result in excessive joint openings. Devices that can dissipate energy have been suggested to reduce joint displacements. Shape memory alloy (SMA) is one of these energy dissipation devices, which is well known for its ability to return to its natural shape after being deformed. Several cases of bridges and different conditions of seismic events are modeled and tested using developed software programs in MATLAB to show the efficiency of using SMA inside bridge joint openings. These models include the case of two adjacent frames with SMA inside them (2�frames), the case of multi�frames with constant hysteretic SMAs between every two of them (N�frames), the case of multi�frames with constant hysteretic SMAs taking the delay of seismic forces between frames into consideration (delay), and the case of variable masses of bridge frames. Also, parametric studies are performed to show the impacts of all parameters of bridge frames and SMA retrofit devices on seismically joint openings. The results show that the superelastic SMA device plays a huge role in controlling bridge opening and enables limiting the joint width of all models during earthquakes with different values reaching 60% in some cases depending on bridge frame properties, ground motion characteristics, and the hysteretic properties of SMA devices

Optimal hysteresis of shape memory alloys for eliminating seismic pounding and unseating of movement joint systems

Bridge structures adapt to movement through the addition of joint systems that accommodate anticipated movement due to temperature variations or earthquakes, thereby relieving stress on the bridge structure. Shape memory alloys (SMAs) have been proposed to limit joint displacements because of their ability to dissipate seismic energy and restore their original shape. A parametric study is conducted in this study using computer simulations of some advanced MATLAB programs to show the effects of all hysteretic parameters of SMA retrofit devices on seismic joint openings. The results show that SMA hysteretic parameters have a huge effect on SMA efficiency as a restrainer, which is compatible with energy dissipation philosophy, but there are some reversible impacts of some hysteretic parameters in some cases due to the resonance problem and their dependence on other parameters such as natural time period, period ratio, mass ratio, and seismic records. As a result, some design charts are created in this study after more than 200 million trials, taking into account the variation of all key parameters of the structure and the SMA under a suite of historical ground motion records. Moreover, bridge designers can choose optimal SMA hysteresis for a desired opening width, a desired time period, and desired period/mass ratios between adjacent frames with the help of these charts to overcome the two bridge problems of pounding and unseating of bridge decks

Computer simulation for the seismic behaviour of bridge expansion joints enhanced with SMA: Case study

This paper concerns the study of the expansion joints of Benha Bridge under seismic loads. The seismic behaviour of its bridge expansion joints has been enhanced by shape memory alloy (SMA) dampers as a form of energy-dissipation device. SMA can dissipate a part of the input energy from the earthquake by generating a counterforce for the induced seismic force, allowing the opportunity to control the joint width and overcome pounding and unseating problems. In this research, MATLAB programs are developed to calculate the joint width responses in the two cases of without SMA and with SMA control devices embedded between adjacent bridge frames, which are modeled as a single degree of freedom system for each frame. Benha Bridge is the subject of this case study, which aims to check and validate the SMA parameter values that their charts have introduced from earlier research and to improve the seismic behaviour of bridge expansion joints by eliminating unseating and pounding problems. The results show that SMA dampers are able to control the joint width and absorb the excess forces caused by nearby expansion joint overlap. Furthermore, SMA design charts are applicable for bridges of multiple frames when they are homogenous in time periods